High frequency deep brain stimulation of the subthalamic nucleus (STN DBS) dramatically ameliorates most but not all symptoms of Parkinson[unreadable]s disease (PD). STN DBS exerts a powerful influence over two nuclei that regulate eye (substantia nigra pars reticulata (SNpr)) and limb (globus pallidus internus (GPi)) motor control. As such, STN DBS should influence eye-hand coordination, and this observation is supported by our preliminary data. Despite the fact that STN DBS improves the motor signs of PD, there is mounting evidence that STN DBS can impair performance of tasks that require using memory and use frontostriatal circuits, especially when bilateral STN DBS is used. As such the long-term objective of the application continues to be the study of the positive and negative effects of STN DBS in humans. We will pursue three specific aims. Aim 1 will test the hypothesis that bilateral STN DBS improves the performance of visually guided eye movements (Aim 1A) and visually guided hand movements (Aim 1B) more than unilateral STN DBS or being off STN DBS. In this aim, there are no memory requirements since targets for both eye and hand moments are always visible. Aim 2 will test the hypothesis that unilateral STN DBS can improve selected measures of performance of memory-guided saccades (Aim 2A) and memory guided movements (Aim 2B) more than bilateral STN DBS or being off STN DBS. The idea behind this aim is that bilateral STN DBS adversely affects dorsolateral prefrontal cortex and this interferes with performance. We also test the hypothesis that both unilateral STN DBS and bilateral STN DBS have a greater effect on eye-hand coordination than conventional dopaminergic medication. Aim 3 will test the hypothesis that three years of chronic stimulation will improve movement speed but not coordination of eye-hand movements. The outcome of these studies will meet a critical need in clinical neurology and basic neurophysiology by assessing the extent to which unilateral STN DBS, bilateral STN DBS, and dopaminergic medication affects eye-hand coordination in PD in both the short and long term.